Remove TYPE_SEARCH_DIDUPDATEINDEX event

Summary:
Ref T9979. This event had one weird callsite and no known third-party callers. It can be done more cleanly as an extension, now.

This index is used to allow us to "Group By: Project" in Maniphest without joining into the Projects database.

Test Plan:

• Ran a query with "Group By: Project" in Maniphest.
• Renamed project "Apples" to "Zebras".
• Reloaded page.
• UI properly moved "Zebras" tasks to the bottom of the list.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9979

Differential Revision: https://secure.phabricator.com/D14836